Winding its way past one of Lalibelas rock churchescarved from the regions soft volcanic tuff some 800 years agoa funeral procession cuts a white swath across the denuded landscape. Once a rich agricultural region, these hills are now exhausted by overfarming. Lalibelans rarely terrace the hillsides, a system that farmers in other parts of the mountainous north use to reduce erosion. Compounding the problem: Long dry spells followed by heavy rains soak Ethiopia for months each summer.